In recent years mirrors have been used to reflect solar rays upon a fixed target. It is necessary, however, to mount and drive such mirrors at one half the earth's rotational period which will then provide a stationary reflected beam. It is usual in such installations to point one axis of the mounting toward the celestial pole and another longitudinal axis of the mirror frame tiltable in declination for seasonal changes.
Since the angle of incidence of arriving light onto the reflective surface of the mirror must always be equal to the angle of reflected light leaving the mirror, the axis of the mounting must be aligned with the polar axis of the earth and must be driven at the rate of one revolution in 48 hours. It is, therefore, understood that while daylight will occupy a 12 hour period, more or less depending on seasonal solar position, actual mirror movement is therefore only ninety degrees to hold the reflected beam on target. It has been customary for this polar axis with the mirror to then be either manually reset or decoupled from the 48 hour rate and moved backward by rather elaborate and expensive devices and linkages.
Although such heliostat drives appear simple, their movements and precise relocation mechanism to pick up and track solar rays each morning has required expensive additions which disqualifies their use as a production item for use by the general public.